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**Session 71 - Stellar Activity/Starspots.**

*Display session, Thursday, June 13*

*Tripp Commons, *

## [71.09] Modeling Magnetic Flux Emergence in HD 106225

*M. J. Wills, E. E. DeLuca (SAO), D. B. Guenther (St. Mary's)*
Using a ``thin flux tube'' approximation proposed by Spruit (1981),
and working with a numerical simulation previously used to model solar
magnetic flux dynamics, we attempt to create magnetic flux tube
emergence in HD 106225, a rapidly rotating subgiant star, which has
been observed to have both x-ray emission and starspots. Initial
attempts, placing the stellar dynamo at the base of the convection
zone, as has been done in solar modeling, were unsuccessful. Fisher,
McClymont, amp; Chou (1991) show that, if the pressure scale height at
the base of the convection zone is a significant fraction of the
radius at that point (\Lambda/R > 0.3), the magnetic tension force
increases faster than the buoyancy as the tube is stretched, and no
rise occurs from a tube anchored at the base of the convection zone.
However, Spruit amp; van Ballegooijen (1982a, b) prove that, for stars
with sufficiently deep convection zones, it is possible to create a
buoyantly stable flux tube in the convection zone itself. The
stability of a given mode again depends on the value of \Lambda/R at
a given radius. If \Lambda/R > 0.3, a flux tube is able to maintain
null buoyancy in the convection zone proper.

Using Spruit amp; van Ballegooijen's solutions, we are able to run
numerical simulations that model stable flux tubes in the convection
zone. We have also been able to create the rise of a magnetic flux
perturbation by placing the base of the ring at a stable convective
radius with the perturbation extending to a more buoyant radius.
Initial attempts have been based on a simplified model, placing a flux
tube at zero latitude with no rotation. We also attempt simulations
which allow for flux rise at non-zero latitudes and include Coriolis
force. Using these results, we examine the implications that such a
magnetic field pattern has for the stellar dynamo.

**Program
listing for Thursday**